Hidden Toxic Metals in Nigerian Gold Mining Soils Pose Cancer Risk to Children

In the dusty gold workings of Rafin Gora, in Nigeria’s Katsina State, the ground itself may be quietly telling a story of danger. A new study published in Environmental Science and Pollution Research has measured nine potentially toxic metals in soils around an artisanal gold mining site and calculated, using internationally accepted risk models, what those concentrations could mean for the health of people living and working nearby. The findings are nuanced: most of the landscape shows little sign of contamination, but localized hotspots of arsenic and chromium are driving a cancer risk that, while below official intervention limits, is far from negligible—especially for children, whose small bodies and hand-to-mouth habits make them disproportionately vulnerable.

The research team, led by Lawal Zubairu of the Sino-French Institute of Nuclear Engineering and Technology at Sun Yat-sen University, together with colleagues at the Nigeria Atomic Energy Commission’s training institute, collected thirty soil samples from across the Rafin Gora mining area. Back at the laboratory of the National Animal Production Research Institute in Zaria, the samples were digested and analyzed by flame atomic absorption spectrophotometry, a workhorse technique that atomizes the sample in a flame and measures how much light each metal absorbs, allowing precise quantification of cadmium, cobalt, chromium, copper, manganese, nickel, lead, arsenic, and zinc. The team then ran the numbers through a battery of established pollution indices and the United States Environmental Protection Agency’s human health risk models.

The pollution indices tell a story of contamination that is real but patchy. The contamination factor, which compares the concentration of each metal in a sample to its background level, revealed that cadmium, arsenic, and zinc showed localized enrichment—meaning that at certain sampling points, human activity had clearly elevated these metals above natural levels. The geoaccumulation index, a logarithmic scale introduced by Müller in 1969 to grade pollution intensity in sediments, classified more than ninety percent of the samples as unpolluted. Yet the pollution load index, which integrates the contamination factors of all measured metals into a single site-level value, exceeded one at most locations, a threshold that signals overall anthropogenic influence rather than purely geological origin.

Ecologically, the news is relatively reassuring. The ecological risk index, originally developed by Hakanson in 1980 for aquatic pollution control, weighs each metal’s toxicity and abundance to estimate the potential harm to ecosystems. Across all sampling locations at Rafin Gora, this index indicated low ecological risk. In other words, the soil ecosystem itself is not yet in crisis. But ecological risk and human health risk are not the same thing, and it is on the human side of the ledger that the study’s most consequential findings emerge.

Using the USEPA’s risk assessment framework, the researchers calculated chronic daily intake values for each metal through three exposure pathways: ingestion of soil particles, inhalation of dust, and dermal contact with soil. The result was unambiguous. Ingestion dominated as the exposure route, and children absorbed doses five to ten times higher than adults. This is not surprising to exposure scientists: children play on the ground, put dusty hands and objects in their mouths, and ingest far more soil per kilogram of body weight than adults do. In a mining village where tailings and crushed ore are scattered across living spaces, that behavioral difference translates directly into a chemical dose difference.

When the researchers summed the hazard quotients—the ratio of each metal’s estimated intake to its reference dose, the level below which no adverse effect is expected—into a hazard index, the values came out at 0.026 for adults and 0.139 for children. Both sit below unity, the conventional line separating acceptable from unacceptable non-carcinogenic risk. Within those totals, however, chromium and arsenic contributed the largest shares of both the hazard quotient and the intake, marking them as the metals that matter most at this site. Cadmium, lead, and the others, despite their fearsome reputations, played comparatively minor roles in the overall risk picture at Rafin Gora.

The carcinogenic risk calculation is where the study acquires its edge. Arsenic and chromium are both recognized human carcinogens, and the USEPA models assign them slope factors that convert chronic intake into a lifetime probability of cancer. The total carcinogenic risk came to 3.66 × 10⁻⁶ for adults and 6.79 × 10⁻⁶ for children. To put those numbers in context: the widely used acceptable upper limit for regulatory purposes is 1 × 10⁻⁴, or one additional cancer case per ten thousand people, and both values fall comfortably below it. But the threshold of negligible risk is conventionally set at 1 × 10⁻⁶, one in a million, and both values—particularly the children’s figure, nearly seven times that level—exceed it. The authors conclude that locally enriched arsenic and chromium drive a non-negligible cancer risk, especially for children.

The Rafin Gora findings resonate with a broader and often tragic pattern across Nigeria’s artisanal gold mining belt. Artisanal and small-scale gold mining is a lifeline for millions of people in West Africa, but it frequently proceeds without environmental safeguards, leaving crushed ore, tailings, and contaminated dust in intimate contact with communities. Previous Nigerian studies have documented heavy metal contamination around artisanal sites in Zamfara, Niger, Osun, and Nasarawa states, and the 2010 Zamfara lead poisoning epidemic—which killed hundreds of children and was traced to lead-rich ores processed inside village compounds—remains one of the starkest demonstrations of what unregulated ore processing can do. The Rafin Gora study adds a carefully quantified data point to this regional picture, showing that even where acute poisoning is absent, chronic low-level exposure can quietly accumulate statistical risk.

Methodologically, the study also illustrates both the power and the limits of standard risk assessment. The USEPA models rely on default exposure assumptions—soil ingestion rates, body weights, exposure frequencies—that are drawn largely from Western datasets and may not perfectly match the realities of rural Nigerian life. Moreover, total metal concentration is not the same as bioavailable metal: only the fraction of a metal that dissolves in the gut can actually be absorbed, and that fraction varies with the metal’s chemical form, or speciation. The authors explicitly recommend that future work incorporate bioaccessibility testing and speciation analysis, which would refine the risk estimates and could either temper or sharpen the current conclusions. They also call for practical mitigation at the site itself, including dust suppression to cut the dominant ingestion and inhalation pathways, and soil remediation to remove or immobilize the enriched arsenic and chromium.

For the people of Rafin Gora, the message of this research is neither panic nor complacency. The soils of the mining area are, by the standard indices, mostly unpolluted, the ecological risk is low, and the non-cancer hazard indices sit safely below regulatory thresholds. Yet the same measurements reveal pockets of arsenic and chromium enrichment that push lifetime cancer risk above the level scientists consider negligible, with children bearing the heaviest burden. In communities where gold mining is both livelihood and hazard, that combination argues for targeted, inexpensive interventions—wetting down dusty paths, keeping children’s play areas clear of tailings, remediating the worst hotspots—rather than wholesale abandonment of the mines. It is a reminder that in environmental health, the dose and the exposed population matter as much as the poison, and that careful measurement is the first step toward protecting the most vulnerable.

Subject of Research: Heavy metal contamination and human health risk assessment in soils of an artisanal gold mining area in Katsina State, Nigeria

Article Title: Health risk assessment of heavy metals exposure in soil at Rafin Gora artisanal gold mining area, Nigeria

Article References: Zubairu, L., Mingliang, K., Xueqing, Y., & Raza, K. (2026). Health risk assessment of heavy metals exposure in soil at Rafin Gora artisanal gold mining area, Nigeria. Environmental Science and Pollution Research, 33(30), 15865-15882. https://doi.org/10.1007/s11356-026-38155-3

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38155-3

Keywords: heavy metals, artisanal gold mining, soil pollution, health risk assessment, arsenic, chromium, Nigeria, children's health, carcinogenic risk, USEPA models, environmental pollution, Katsina State